Major internal diff: single cell vs. multicellular

[Pythagorean]

What are some of the major (if not the major) difference(s) between the inside of a single specialized cell (like a muscle cell or a skin cell) and a single-celled organism.

Does a single-celled organism have the capacity to make more "decisions" than a muscle cell?

 

[Andy Resnick]

Are you asking about anatomical or physiological differences?

 

[cesiumfrog]

I think both kinds of cell "make decisions" (or are constructed in such a way as to react differently in different circumstances). And even single-celled organisms communicate with other cells.

I'm not sure whether healthy single-celled organisms ever abort all further growth/reproduction (whereas in many multicellular organisms, some cells even commit seppuku). Could that be the defining difference? It would naively make sense, judging multicellularity on whether cells entrust their genetic lineage to be furthered by the greater organism rather than passed on individually. I'm sure there's things like slime moulds (and bee hives) that will challange any hard distinctions though..

 

[Pythagorean]

Are you asking about anatomical or physiological differences?

Well, both now that you ask. I was thinking physiological mostly. I know that independent cells have flagellum for motion. That something I wouldn't expect to see in a specialized mammal cell. So some of the molecular machinery will be different.

What about digestion, for instance?

Or what about the protein coding and signaling? Could a skin cell become a successful independent cell if we gave it the the instruction set from a comparable single celled organism?

 

[Pythagorean]

I think both kinds of cell "make decisions" (or are constructed in such a way as to react differently in different circumstances). And even single-celled organisms communicate with other cells.

I'm not sure whether healthy single-celled organisms ever abort all further growth/reproduction (whereas in many multicellular organisms, some cells even commit seppuku). Could that be the defining difference? It would naively make sense, judging multicellularity on whether cells entrust their genetic lineage to be furthered by the greater organism rather than passed on individually. I'm sure there's things like slime moulds (and bee hives) that will challange any hard distinctions though..

This is the more general interest of mine from which this question arises. I've watched several movies of Slime molds :P

 

[Andy Resnick]

Well, both now that you ask. I was thinking physiological mostly. I know that independent cells have flagellum for motion. That something I wouldn't expect to see in a specialized mammal cell. So some of the molecular machinery will be different.

Sperm swim, airway and oviduct epithelia move mucus using motile cilia (which is identical to a flagellum). The blastocyst uses nodal cilia (which twirl) to differentiate left and right.

Most mammalian cells have a primary cilium which (it is hypothesized) is used to sense the environment. The mammalian cilium is identical to the bacterial flagellum, and the protein machinery associated with the growth, maintenance, and secondary signalling pathways is highly conserved.

There's obvious differences between prokayotic and eukaryotic cells- in addition to size (bacteria are much smaller than protozoans). The presence or absence of a nuclear membrane, the structure of the cell wall (gram positive or negative), but metabolic pathways are conserved, DNA is DNA everywhere, ribosomes are conserved, the ER is conserved, etc. etc. Bacteria do not have mitochondria.

What about digestion, for instance?

Or what about the protein coding and signaling? Could a skin cell become a successful independent cell if we gave it the the instruction set from a comparable single celled organism?

Groups are trying to do as you suggest- turn a differentiated cell into an undifferentiated (stem) cell.

My knowledge here is limited, but cesiumfrog's suggestion seems reasonable: a major difference between a protozoan and a mammalian cell is differentiation, which relates both to function and to apoptosis- a terminally differentiated cell no longer divides. My renal cells (well, the ones I use in the lab) are kept undifferentiated until sufficient numbers grow up, and then I allow them to differentiate, at which point they gain function (vector salt transport, growth of a cilium) and lose the ability to grow and divide.

 

[Monique]

Gee, it would depend what you are looking a. A major difference would be the set of genes that is expressed and the way the chromatin is modeled. When a cell differentiates its developmental potential becomes more limited, this is illustrated by a ball rolling downhill through different valleys (Waddington canal). The differentiation is typical for multi-cellular organisms.

 

[Pythagorean]

Sperm swim, airway and oviduct epithelia move mucus using motile cilia (which is identical to a flagellum). The blastocyst uses nodal cilia (which twirl) to differentiate left and right.

Most mammalian cells have a primary cilium which (it is hypothesized) is used to sense the environment. The mammalian cilium is identical to the bacterial flagellum, and the protein machinery associated with the growth, maintenance, and secondary signalling pathways is highly conserved.

There's obvious differences between prokayotic and eukaryotic cells- in addition to size (bacteria are much smaller than protozoans). The presence or absence of a nuclear membrane, the structure of the cell wall (gram positive or negative), but metabolic pathways are conserved, DNA is DNA everywhere, ribosomes are conserved, the ER is conserved, etc. etc. Bacteria do not have mitochondria.

Thank you for your reply, Andy, you've pretty much answered the OP. I was silently ignoring prokaryotes.

So even eukaryote bacteria don't have mitochondria... I guess that would make sense for the the endosymbiotic theory (hey, wouldn't that make the eukaryote w/ mitochondria multi-cellular? :P)

A major difference would be the set of genes that is expressed and the way the chromatin is modeled. When a cell differentiates its developmental potential becomes more limited, this is illustrated by a ball rolling downhill through different valleys (Waddington canal). The differentiation is typical for multi-cellular organisms.

Balls rolling down hills, you're speaking my language.

I suspected gene expression would have to be different. Is the underlying gene pool nearly an overlap between the two cases?